Docker 13:09 / 15.07.2021
The official Nextcloud image for Docker already includes options to automatically obtain a certificate from Let's Encrypt – to do this, just define environment variables LETSENCRYPT_HOST and LETSENCRYPT_EMAIL in the Docker Compose file. But this is not possible for the PHP-FPM version of the image for obvious reasons. Of course, you can solve everything with the container proxy, for example nginx-proxy, but if you need to get Nextcloud up and running quickly just to get acquainted with its functionality and SSL is a must for most of the functionality, then perhaps a simpler solution (but maybe not quite right).
Here is my solution for raising a fully functional Nextcloud instance on Docker, based on an image with PHP-FPM and with SSL from Let's Encrypt.